This invention relates to tape tensioning apparatus, and particularly to tensioning apparatus in which continous sensing of the instantaneous length of a tape loop is provided.
In the magnetic tape transport art, it is of great importance to maintain the tape tension at a predetermined value during the play and record modes in order to stabilize the actual speed of the tape across the heads. A similar but slightly less rigorous requirement obtains during the fast-forward and fast-rewind modes in order to prevent slack and throwing of the tape or breaking thereof.
To this end, it is common practice to guide the tape in a loop the length of which is sensed by means such as spring-loaded tension arms engaging the tape loop segment between tape moving and anchoring means, such as the capstan and supply reel, for play and record modes; or between the two reels, for fast forward or rewind modes. The transport control and servo system determine the length of tape to be maintained between the anchoring means, and the tension arm senses the actual length in accordance with its own rotational displacement, as the tape segment length changes, and signals this information to the control servo system; the system continously regulates the tape segment length by operating the tape moving and anchoring means until the desired length is achieved. The tension arm thus has a different position for each mode of operation, and as the arm moves from one of these positions to another, a different spring, or set of springs, is brought into play to establish the tension level desired for the corresponding mode.
In place of spring loaded tension arms, the prior art often uses tape-loop vacuum columns or linear-loop pulley systems with loop-length sensing means. Examples of various combinations of such structures may be found in e.g. U.S. Pat. Nos. 3,836,089; 3,862,724, and 3,889,895.
In such prior art apparatus, however, a common problem is that the loop-length sensing sub-assembly is not structurally integral with the tape loop-forming sub-assembly so that the two sub-assemblies must be assembled and calibrated in three operations during the factory assembly of the machine; and subsequent replacement of a defective or failed sensing means in the field requires a re-calibration of the two sub-assemblies, requiring the presence of a factory specialist.
Accordingly, it is an object of the present invention to provide a tape-loop forming and loop-length sensing apparatus that is more easily and inexpensively assembled during manufacture, and replaced or repaired in the field.